Ab initio potential energy surface and second virial coefficient for Asp-His-Ser trimer

HF level of ab initio calculations with basis-set 6-31G including full counterpoise correction hasbeen applied to compute the AspHis potential with the Ser and HisSer potential with the Asp inAspHisSer trimer. The potential energy surface has a minimum of -16.765 kcal/mol in R1=1.912nm and R2=2.719 nm. The optimum computed curves for two interactions were fitted withintermolecular pair potential models, including of Lennard-Jones, Kihara, Buckingham Exp-6 andBuckingham Exp-6-8 potentials. The Buckingham exponential potentials gave the best fit. Thesepotentials have been used to calculate the second virial coefficient for AspHis-Ser and Asp-HisSerinteractions. As we expected B2 for Asp-HisSer interaction was more negative from AspHis-Serinteraction.